> Hello, from discussion in https://github.com/openjdk/jdk/pull/3464 and > https://github.com/openjdk/jdk/pull/2212 it appears, that in `j.l.Class` > expressions like > > String str = baseName.replace('.', '/') + '/' + name; > > are not compiled into invokedynamic-based code, but into one using > `StringBuilder`. > > This happens due to some bootstraping issues. Currently the bytecode for the > last (most often used) branch of `Class.descriptorString()` looks like > > public sb()Ljava/lang/String; > L0 > LINENUMBER 21 L0 > NEW java/lang/StringBuilder > DUP > INVOKESPECIAL java/lang/StringBuilder.<init> ()V > ASTORE 1 > L1 > LINENUMBER 23 L1 > ALOAD 1 > LDC "a" > INVOKEVIRTUAL java/lang/StringBuilder.append > (Ljava/lang/String;)Ljava/lang/StringBuilder; > POP > L2 > LINENUMBER 24 L2 > ALOAD 1 > LDC "b" > INVOKEVIRTUAL java/lang/StringBuilder.append > (Ljava/lang/String;)Ljava/lang/StringBuilder; > POP > L3 > LINENUMBER 26 L3 > ALOAD 1 > INVOKEVIRTUAL java/lang/StringBuilder.toString ()Ljava/lang/String; > ARETURN > > Here the `StringBuilder` is created with default constructor and then expands > if necessary while appending. > > This can be improved by manually allocating `StringBuilder` of exact size. > The benchmark demonstrates measurable improvement: > > @State(Scope.Benchmark) > @BenchmarkMode(Mode.AverageTime) > @OutputTimeUnit(TimeUnit.NANOSECONDS) > @Fork(jvmArgsAppend = {"-Xms2g", "-Xmx2g"}) > public class ClassDescriptorStringBenchmark { > > private final Class<?> clazzWithShortDescriptor = Object.class; > private final Class<?> clazzWithLongDescriptor = getClass(); > > @Benchmark > public String descriptorString_short() { > return clazzWithShortDescriptor.descriptorString(); > } > > @Benchmark > public String descriptorString_long() { > return clazzWithLongDescriptor.descriptorString(); > } > } > > > > original > -Xint > Mode Score Error > Units > descriptorString_long avgt 6326.478 ± 107.251 > ns/op > descriptorString_short avgt 5220.729 ± 103.545 > ns/op > descriptorString_long:·gc.alloc.rate.norm avgt 528.089 ± 0.021 > B/op > descriptorString_short:·gc.alloc.rate.norm avgt 232.036 ± 0.015 > B/op > > -XX:TieredStopAtLevel=1 > Mode Score Error > Units > descriptorString_long avgt 230.223 ± 1.254 > ns/op > descriptorString_short avgt 164.255 ± 0.755 > ns/op > descriptorString_long:·gc.alloc.rate.norm avgt 528.046 ± 0.002 > B/op > descriptorString_short:·gc.alloc.rate.norm avgt 232.022 ± 0.001 > B/op > > full > Mode Score Error > Units > descriptorString_long avgt 74.835 ± 0.262 > ns/op > descriptorString_short avgt 43.822 ± 0.788 > ns/op > descriptorString_long:·gc.alloc.rate.norm avgt 504.010 ± 0.001 > B/op > descriptorString_short:·gc.alloc.rate.norm avgt 208.004 ± 0.001 > B/op > > ------------------------ > patched > -Xint > Mode Score Error > Units > descriptorString_long avgt 4485.994 ± 60.173 > ns/op > descriptorString_short avgt 3949.965 ± 278.143 > ns/op > descriptorString_long:·gc.alloc.rate.norm avgt 336.051 ± 0.004 > B/op > descriptorString_short:·gc.alloc.rate.norm avgt 184.027 ± 0.010 > B/op > > -XX:TieredStopAtLevel=1 > Mode Score Error > Units > descriptorString_long avgt 185.774 ± 1.100 > ns/op > descriptorString_short avgt 135.338 ± 1.066 > ns/op > descriptorString_long:·gc.alloc.rate.norm avgt 336.030 ± 0.001 > B/op > descriptorString_short:·gc.alloc.rate.norm avgt 184.019 ± 0.001 > B/op > > full > Mode Score Error > Units > descriptorString_long avgt 42.864 ± 0.160 > ns/op > descriptorString_short avgt 27.255 ± 0.381 > ns/op > descriptorString_long:·gc.alloc.rate.norm avgt 224.005 ± 0.001 > B/op > descriptorString_short:·gc.alloc.rate.norm avgt 120.002 ± 0.001 > B/op > > Same can be done also for Class.isHidden() branch in Class.descriptorString() > and for Class.getCanonicalName0()
Сергей Цыпанов has updated the pull request incrementally with one additional commit since the last revision: 8266622: Remove pointless String.substring() call ------------- Changes: - all: https://git.openjdk.java.net/jdk/pull/3903/files - new: https://git.openjdk.java.net/jdk/pull/3903/files/7c26095e..641f5273 Webrevs: - full: https://webrevs.openjdk.java.net/?repo=jdk&pr=3903&range=01 - incr: https://webrevs.openjdk.java.net/?repo=jdk&pr=3903&range=00-01 Stats: 1 line in 1 file changed: 0 ins; 0 del; 1 mod Patch: https://git.openjdk.java.net/jdk/pull/3903.diff Fetch: git fetch https://git.openjdk.java.net/jdk pull/3903/head:pull/3903 PR: https://git.openjdk.java.net/jdk/pull/3903
